There are some people who use chillers for their kois in Singapore, though it may not be bulking up fish, it can be used by fish farms to acclimatize fish more easily and faster during shipments as the fish are shipped in cold water.

Actually koi can easily adapted to temperature around 30 degrees celcius with no problem at all. What hardcore hobbyists concern is the oxygen concentrations. The cooler the water, the more oxygen molecules can be retained in the water. Koi thrives well with more oxygen in the water. Thus, people go to the extent of installing chillers for koi pond, which is a great burden on electrical bill. A much cheaper alternative is to install more air pump outlets in the pond, improving the aeration.

Actually koi can easily adapted to temperature around 30 degrees celcius with no problem at all. What hardcore hobbyists concern is the oxygen concentrations. The cooler the water, the more oxygen molecules can be retained in the water. Koi thrives well with more oxygen in the water. Thus, people go to the extent of installing chillers for koi pond, which is a great burden on electrical bill. A much cheaper alternative is to install more air pump outlets in the pond, improving the aeration.

Actually koi can easily adapted to temperature around 30 degrees celcius with no problem at all. What hardcore hobbyists concern is the oxygen concentrations. The cooler the water, the more oxygen molecules can be retained in the water. Koi thrives well with more oxygen in the water. Thus, people go to the extent of installing chillers for koi pond, which is a great burden on electrical bill. A much cheaper alternative is to install more air pump outlets in the pond, improving the aeration.

Agree bro.

What I did, besides airpump, is the cheap alternative of blowing air across the water surface using a powerful fan. Managed to reduce temperature by 2 to 3 degress over night- so by morning the temperature is around 27+ degrees.

I expect lower temperature when the cooler season arrives at the end of the year.

Only issue with fan is the need to constantly look out for bad weather if pond is outdoors.